Why can a material glow in color after the light is gone?
Some materials store energy from light and release it slowly afterward, a process called phosphorescence. In a recent study, a cellulose-based material was tuned so that its molecules, when spread apart, gave off blue phosphorescence, while clumps of the same molecules gave off green [1]. A mixture of separated molecules and clumps produced phosphorescence whose color changed depending on the wavelength of the exciting light [1].
The striking part is that these materials could be excited by ordinary visible light and then emit green or yellow phosphorescence once that light was turned off [1]. That means the color you perceive is generated by the material's response, not simply by the incoming light. The researchers used this effect to make phosphorescent inks for anti-counterfeiting patterns and information codes [1]. So color, in this practical sense, is a property of how a material handles light—not something that belongs only to the visible spectrum itself.
Could color be experienced without seeing it?
A separate philosophical paper asks whether color experiences are necessarily visual. Many people assume that colors, unlike shapes, can only be seen—shapes can be seen or felt, but colors supposedly only enter experience through the eyes [2]. The author argues there is no good reason for this restriction and concludes that if colors are mind-independent features of the world, they can probably be experienced non-visually [2].
This is a claim about the nature of color experience, not a laboratory demonstration. The paper explicitly frames the conclusion as conditional: it holds if you already believe colors exist independently of minds, and the author argues the result is not absurd [2]. It does not show that people actually feel colors, only that the usual assumption that color is exclusively visual may be unjustified.
What does “unique to visible light” mean here?
The two lines of evidence answer slightly different versions of the question. In the materials science sense, color is not unique to visible light because a substance can be excited by visible light and then emit colored phosphorescence on its own [1]. The color is a product of the material's behavior, and the study shows it can be tuned by changing how the molecules aggregate [1].
In the philosophical sense, the question is whether color experience is limited to vision. The argument suggests that if colors are real, mind-independent features, then there is no principled reason they could only be seen [2]. Neither paper claims that colors exist outside light in some physical sense; together they widen the answer beyond the simple idea that color equals visible light.
What is still unresolved?
The phosphorescence study demonstrates a working material and its applications, but it does not settle broader questions about what color fundamentally is [1]. The philosophical paper offers an argument rather than an empirical test, and its conclusion depends on the premise that colors are mind-independent [2]. So the practical answer is clear—color can arise from visible-light-driven phosphorescence—while the deeper question of whether color could be experienced through other senses remains a matter of argument rather than demonstration [1][2].
Sources used in this answer
Aggregation-regulated room-temperature phosphorescence materials with multi-mode emission, adjustable excitation-dependence and visible-light excitation
Cellulose-based phosphorescent materials can emit blue, green, or tunable color depending on molecular aggregation, and aggregated forms emit green or yellow phosphorescence after visible-light excitation is turned off.
Are colors only visible?
The paper argues that if colors are mind-independent, there is no good reason to think they can only be experienced visually, so they could probably be experienced non-visually.